Vt fuse with inherent capacity for pd action when on a normal approach collision course

ABSTRACT

1. An ordnance fuze for an aerial missile comprising first circuit means for generating and transmitting a continuous wave radiofrequency signal into the surrounding spatial area, second circuit means for receiving a target reflected portion of said radiofrequency signal, third circuit means coupled to said first and second circuit means for developing an output signal having a frequency corresponding to the instantaneous frequency difference between said transmitted radiofrequency signal and said target reflected portion thereof, fuze firing means, fourth circuit means including a low pass filter and detector for effecting detonation of the fuze by said firing means only in response to said output signal when said output signal has a frequency indicative of a noncollision course by the missile, and impact responsive means for effecting detonation of the fuze by said firing means when the missile is on a target collision course.

United States Patent [72] Inventors SamuelW.Lichtman Riverside;

Donald J. Adrian, Arlington, both of Calif. [21] Appl. No. 565,746 [22] Filed Feb. 15, 1956 [45] Patented Oct. 19, I971 The United States of America as represented by the Secretary of the Navy [73] Assignee [54] VT FUZE WI'I'I-I INI-IERENT CAPACITY FOR PD ACTION WHEN ON A NORMAL APPROACH Electronics, Feb. 1946 page 105 Proximity Fuzes for Artillery by H. Selridge Journal of Research of the National Bureau of Standards Research Paper 1723, Volume 37, page 5 July 1946, Radio Proximity Fuze Design, by W. S. Henmon, Jr. & C. Brunetti, Radio News, Dec. 1945, The proximity Fuze, page 155. Product Engineering, November 1945, Proximity Fuze, page 783 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas H. Webb Att0rneys-G. J. Rubens and J M. St. Amand CLAIM: 1. An ordnance fuze for an aerial missile comprising first circuit means for generating and transmitting a continuous wave radiofrequency signal into the surrounding spatial area, second circuit means for receiving a target reflected portion of said radiofrequency signal, third circuit means coupled to said first and second circuit means for developing an output signal having a frequency corresponding to the instantaneous frequency difference between said transmitted radiofrequency signal and said target reflected portion thereof, fuze firing means, fourth circuit means including a low pass filter and detector for effecting detonation of the fuze by said firing means only in response to said output signal when said output signal has a frequency indicative of a noncollision course by the missile, and impact responsive means for effecting detonation of the fuze by said firing means when the missile is on a target collision course.

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INVENTORS. D. J. ADRIAN S. W. LICHTMAN ATTORNEYS VT FUZE WITII INIIERENT CAPACITY FOR PD ACTION WI-IEN ON A NORMAL APPROACH COLLISION COURSE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The invention relates to a fuse and more particularly to a proximity fuse with an intrinsic capacity for point detonation operation when on a normal approach collision course.

The conventional proximity fuse fires by proximity to a target, however this type of fuse does not distinguish between a noncollision and a collision course, since the fuse responds to the gross features of the detected return signal from an unmodulated CW type of transmitted energy and fires when the detected return signal reaches an optimum value.

The present invention is based on the fact that the return signal may be resolved into low-frequency and high-frequency components and the low-frequency components do not occur to any substantial extent during a collision course normal to the target aircraft whereas they do occur on a noncollision course and can be utilized for proximity actuation of the fuse.

' One preferred embodiment of the present invention is illustrated herein, wherein an unmodulated CW signal is transmitted from the missile towards the target aircraft and the received signal consisting of the carrier frequency plus the doppler frequency is mixed with the carrier frequency to produce a doppler output consisting of the doppler frequency spectrum produced by the grading of velocities resulting from the difl'erent angles of incidence and reflection of the transmitted energy from different portions of the target aircraft.

During the normal approach this spectrum will consist essentially of a narrow band of frequencies centered around the head on doppler and in the case of a collision course will remain substantially the same until a time just prior to contact, when a relatively wide band of frequencies will appear. In the case of a noncollision course the band of frequencies will spread gradually as the missile approaches the target and will contain a large percentage of relatively high-amplitude lowfrequency components during the time it is passing the missile. In the latter case the low-frequency components will go through a low-pass filter to the firing circuit to actuate the fuse as a proximity fuse, however, in the former case the firing circuit will not have sufficient time to operate on the lowfrequency components, since they occur just prior to contact, and the point detonation contacts will then actuate the firing circuit on contact.

One object of the present invention is to provide a fuse which will be actuated by point detonation when on a normal approach collision course, but will be actuated by proximity action when on a noncollision course.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram illustrating one preferred form of apparatus for implementing the method of the present inventron;

FIG. 2 is a graph representing the intact M-wave or the complete detected return signal from an unmodulated CW type of VT fuse;

FIG. 3 is a graph representing the wave component below 15 percent of the head on doppler frequency;

FIG. 4 is a graph representing the component above 15 percent of the head on doppler frequency;

FIG. 5 is a graph representing the component above 50 percent of the head on doppler frequency;

FIG. 6 is a diagram illustrating the air approach geometry; and

FIG. 7 is a diagram illustrating the spatial distribution of the doppler spectrum.

Referring now to the drawings in detail, FIGS. 2 through 5 are reproductions of actual oscillograms obtained by photographing signature trace waveforms of 'a target aircraft and the output waveforms of wave filters excited from these signature traces.

FIG. 2 represents the intact in-close target returri. signal called the M-wave as received by the fuse from the target aircraft and including all of the components of the doppler frequency spectrum which is produced by the grading ,of velocities associated with scatterers on the target aircraft which receive energy at different incident angles from the fuse transmitter. This spectra is continuum containing frequencies ranging from zero to a maximum value as determined by the particular angles of incidents as illustrated in FIG. 6 which shows the air approach geometry.

FIGS. 2 through 5 illustrate the signal received where the missile is on a noncollision course greater than two wavelengths away from the target aircraft.

THEORY When a fused missile and a target are in close proximity, different areas of the target are moving at different velocities relative to the missile. Specular and diffuse reflection of the radiation then act to produce a signal at the fuse detector out put, which contains a spectrum of doppler frequencies F,,.

Let the passage of a fused missile over a target be represented geometrically as in FIG. 6 The fuse is assumed to be firmly attached to the orthogonal reference frame x'y'z' and to be displaced an amount z from the origin of coordinates. Consider the target as being stationary and to lie in, the x'y' plane and the fuse, together with its frame of reference, to move with velocity in the x direction. The point Q is any reflecting center on the target, r is the distance from the fuse to Q, and a is the angle between r and the fuse trajectory. From FIG. 6 we obtain I cos oz=x'/r, v l) by substituting equation (2) into equation (I and. rearranging the terms we obtain 'V n -U")*=(z') For any horizontal plane (z constant), this equation represents a family of hyperbolas, each curve corresponding to a particular value of a. A particular doppler frequency: is given by f,,=f cos a, where f,, is the head-on doppler frequency. Defining p as the ratio of the observed doppler frequency to the head-on doppler frequency, we may write a cos"p Substituting this expression into equation (3), we obtain 'V m2 "p)(y')=(z') A plot of equation (5), showing the location of reflecting regions as a function of spectral frequency components for an impact parameter of 4)\, appears in FIG. 7. For the impact parameter chosen, FIG. 5 identifies the location of reflecting regions on a target in the xy plane that are responsible for particular spectral terms.

In the oscillogram of FIG. 3, for example, the wave patterns obtained below 15 percent f, would be attributable to reflectors lying in the region between the two lines. Similarly, in the oscillogram or FIGS. 4 and 5 for the high-pass 15 percent f,, and 50 percent f cases, the wave patterns would be identified with reflecting regions lying beyond these respective lines.

The close-in target-signature trace is a complex wave pattern containing a frequency spectrum of components returned from widely dispersed areas of the target surface. Analysis of the signature trace by means of a wave filter furnished evidence for the isolation of components of the wave affiliated with definite regions of the target surface.

The lowest frequency component is attributable to normal reflections from the target (i.e., for perpendicular incidence) and as such contains most of the wave energy. It is closely linked with irregularities of the target surface and, in the case of some traces appears to outline the target features rather clearly. As this spectral region is caused by normal reflections, it is found to be constrained to the region within the target extremities.

Removal of the low-frequency component leaves a resultant wave-envelope of good axial symmetry The envelope of this wave which resembles that of the ideal M-wave from a spherical target, consists generally of a single elliptical wave-envelope configuration.

The high-frequency wave components from the theory that has been presented represent echoes from the extremities of the target. Suppression of spectral components below 50 percent of 1",, usually results in the appearance of three wave groups with maxima occurring near the tail, center, and nose positions of the target as in FIG. 5. For some trajectories the tail apparently does not intercept a sufficient amount of radiation to produce a well-defined wave pattern.

It thus appears that frequency decomposition of the close-in signature trace isolates wave components that contain target resolution information, and this information is utilized in the copending application of S. W. Lichtman, Ser. No. 567,037, filed Feb. 21, 1956, for actuating a proximity fuse at an optimum position with respect to the target.

In the present invention the low-frequency component as illustrated in FIG. 3 is utilized for firing the fuse by proximity action when on a noncollision course passing close to the target.

Since the low-frequency components occur only when the angle a approaches 90, as illustrated in FIG. 6, and this condition only occurs when the missile is passing by the target or just prior to contact when on a collision course, it will be apparent that the signal resulting from the low-frequency components will not provide proximity actuation of the fuse when the missile is on a collision course, and therefore point detonation actuation can be provided to obtain the optimum damage to the target.

As illustrated in FIG. 1, one preferred embodiment of apparatus for carrying out the method of the present invention consists of a master oscillator 11 which sends the basic frequency to the transmitter 12 which transmits the carrier frequency f The same frequency is sent to the mixer 13 where it is mixed with the received signals from the receiver 14 consisting of the carrier frequency f,. plus the spectrum of doppler frequencies F,,. The output of the mixer is a signal containing the beat frequencies F consisting of the complete doppler frequency spectra produced as discussed supra. This signal P, is passed through the low-pass filter 15 which only passes the low-frequency components to the detector 16 and firing circuit 17 for actuation of the fuse on proximity to the target on a noncollision course.

When the missile is on a collision course with a target the signal from the low-pass filter l5 and detector 16 does not arrives in time to actuate the firing circuit 17 before the point detonation contacts 18 are actuated by impact of the missile with the target aircraft.

The low-pass filter 15 is preferably one which will pass only frequencies below approximately 20 percent f where f is the head-on doppler frequency.

It will be apparent that by confining the proximity operation of the fuse to the low-frequency region of the doppler continuum for values of f /f which are much less than 1, preferably in the region between the two p =O.20 lines in FIG. 7, the doppler signal does not exist for a normal approach collision course with the target.

Under these circumstances proximity action is inhibited and point detonation contact fuse operation may be achieved. For all other pass conditions the doppler signal occurs at the point of closest approach to the edge of the target.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: 1. An ordnance fuse for an aerial missile comprising first circuit means for generating and transmitting a continuous wave radiofrequency signal into the surrounding spatial area, second circuit means for receiving a target reflected portion of said radiofrequency signal, third circuit means coupled to said first and second circuit means for developing an output signal having a frequency corresponding to the instantaneous frequency difference between said transmitted radiofrequency signal and said target reflected portion thereof, fuse-firing means, fourth circuit means including a low-pass filter and detector for effecting detonation of the fuse by said firing means only in response to said output signal when said output signal has a frequency indicative of a noncollision course by the missile, and impact-responsive means for effecting detonation of the fuse by said firing means when the missile is on a target collision course.

2. An ordnance fuse for an aerial missile comprising an oscillator circuit for developing a continuous wave signal of a preselected radiofrequency, a transmitter circuit coupled to said oscillator circuit for radiating said developed signal into the surrounding spatial medium, a receiver circuit for intercepting an object reflected portion of said radiated signal, a mixer circuit coupled to said oscillator and receiver circuits for developing a beat frequency output signal correlative to the instantaneous frequency difference between the transmitted and received signals, a firing circuit for effecting detonation of the fuse upon actuation thereof, circuit means including a low-pass filter and a detector intercoupling said mixer and firing circuits for actuating said firing circuit in response to said output signal when said output signal from said mixer circuit, has a beat frequency representative of a noncollision course by the missile, and impact-responsive point-detonating contacts coupled to said firing circuit for effecting actuation thereof upon collision of the missile with a target. 

1. An ordnance fuse for an aerial missile comprising first circuit means for generating and transmitting a continuous wave radiofrequency signal into the surrounding spatial area, second circuit means for receiving a target reflected portion of said radiofrequency signal, third circuit means coupled to said first and second circuit means for developing an output signal having a frequency corresponding to the instantaneous frequency difference between said transmitted radiofrequency signal and said target reflected portion thereof, fuse-firing means, fourth circuit means including a low-pass filter and detector for effecting detonation of the fuse by said firing means only in response to said output signal when said output signal has a frequency indicative of a noncollision course by the missile, and impactresponsive means for effecting detonation of the fuse by said firing means when the missile is on a target collision course.
 2. An ordnance fuse for an aerial missile comprising an oscillator circuit for developing a continuous wave signal of a preselected radiofrequency, a transmitter circuit coupled to said oscillator circuit for radiating said developed signal into the surrounding spatial medium, a receiver circuit for intercepting an object reflected portion of said radiated signal, a mixer circuit coupled to said oscillator and receiver circuits for developing a beat frequency output signal correlative to the instantaneous frequency difference between the transmitted and received signals, a firing Circuit for effecting detonation of the fuse upon actuation thereof, circuit means including a low-pass filter and a detector intercoupling said mixer and firing circuits for actuating said firing circuit in response to said output signal when said output signal from said mixer circuit, has a beat frequency representative of a noncollision course by the missile, and impact-responsive point-detonating contacts coupled to said firing circuit for effecting actuation thereof upon collision of the missile with a target. 